An electrophotographic photoreceptor generally has a flange or a gear flange coupled to either end of a photosensitive drum formed by forming a photosensitive layer on an outer circumferential surface of a conductive substrate. Such photoreceptor is installed in a process cartridge, which is then mounted in an electrophotographic application apparatus such as a copier, a printer, or a facsimile.
The process cartridge is a form of cartridge in which a charging member for direct voltage application (including neutralization) and various other members for performing electrophotographic processes such as development and cleaning are disposed around an electrophotographic photoreceptor and integrally stored. The process cartridge is detachably mounted on an electrophotographic application apparatus and serves a central function in image formation.
An electrophotographic application apparatus mounted with a process cartridge first forms a latent image by exposing an electrophotographic photoreceptor to light in response to image information, the electrophotographic photoreceptor being charged evenly in a charging process. Next, the latent image is developed in a developing process using toner, to form a toner image on the photoreceptor. Further, the toner image is transferred onto a base such as a piece of paper in a transfer process, thereby executing image formation.
The process cartridge system described above has conventionally been used widely in electrophotographic application apparatuses using electrophotographic processes. One of the advantages of such process cartridge is that it almost eliminates need to perform maintenance on the apparatus main body, making the maintainability of the apparatus very simple.
Incidentally, a process cartridge accomplishes the electrophotographic processes by causing the electrophotographic photoreceptor to rotate in response to the rotational driving force from the apparatus main body. In order to transmit the driving force, a flange with a gear or a flange is generally coupled to an edge of the photosensitive drum.
When the gear flange or flange coupled to the photosensitive drum falls off the photoreceptor, or when the coupling portion therebetween is loosened, the driving force is not transmitted, and therefore the rotation of the photoreceptor stops, stopping the function of the apparatus or causing serious accidents such as jittering and other types of image failure. An important technical subject is to ensure long-term reliability in the coupling portion between the gear flange or flange and the photosensitive drum, so that the gear flange or flange is prevented from falling off the photoreceptor or being loosened in the coupling portion.
In addition, poor fitting accuracy between a driven-side power transmission portion of the flange and a drive-side power transmission portion of the apparatus main body disables the transmission of the driving force, resulting in image failure. It is, therefore, important to reliably couple the flange and the photosensitive drum to each other and to keep high rotational accuracy over a long period of time by accomplishing an optimum fitting state in the drive-side power transmission portion and thereby reliably transmitting the rotational driving force.
Regarding the improvement of the driven-side power transmission portion of the flange, Patent Document 1, for example, discloses a technology of improving the rotational accuracy of a photosensitive drum by providing an apparatus main body gear with a predetermined twisted hole, providing one end of the electrophotographic photosensitive drum in a longitudinal direction with a twisted projection, and fitting the twisted hole and the twisted projection together to transmit the rotational driving force.
Patent Document 2 discloses a technology of reliably transmitting the driving force and preventing vibration of the process cartridge by coupling the apparatus main body and the process cartridge to each other by means of a coupling hole and coupling projection of the apparatus main body gear, as well as a projection and an abutting portion coming into external abutment with the projection, which are provided in the apparatus main body and the process cartridge.
Patent Document 3 discloses a technology concerning a developing cylinder with a driven-side power transmission portion of a flange, the shape of the driven-side power transmission portion being improved, and a drive gear, the technology aiming to promptly execute molding of the driven-side power transmission portion.
Patent Document 1: Japanese Patent Application Publication No. H8-328449 (claims, etc.)
Patent Document 2: Japanese Patent Application Publication No. 2001-324845 (claims, etc.)
Patent Document 3: U.S. Pat. No. 6,173,146 (Description)